Bacillus subtilis undergoes differentiation (sporulation) when it encounters nutrient deprivation. Many new proteins are synthesized only during sporulation. The mechanisms by which this bacterium controls the expression of these developmentally regulated genes are not known. We are currently investigating the mechanism(s) controlling one sporulation specific gene, the glucose dehydrogenase gene (gdh). This gene and an uncharacterized gene that precedes gdh comprise an operon that is expressed only during sporulation. The nucleotide sequence and ribosome binding sites have been determined. The promoter is located within a 0.5 kb PvuI region and has been narrowed to be between AluI and PvuI sites. No nucleotide sequence in this fragment matches any of the known promoter sequences of the B. subtilis RNA polymerases. DNA fragments that contain the putative promoter sequence of the gdh operon were inserted in front of plasmid-borne promoter-less genes to determine which sequences are necessary for sporulation control of gdh. A comparison between the B. subtilis DNA sequence and the B. megaterium amino acid sequence showed how many and what type of mutations occurred during the evolution of gdh.